Analysis of biological phenomena on the cell level and diagnosis of diseases on the molecular level require the detection of a specific nucleic acid sequence. To this end, a modified DNA oligomer having a functional molecule, such as a fluorescent dye or a biologically active substance, introduced thereto is used in various experiments.
In chemical modification of a DNA oligomer, a reactive site for modification is introduced to an end or a base of the nucleic acid.
In particular, if a reactive site can be introduced to a base of a nucleic acid, it becomes possible to introduce different functional molecules to an end and the base of the nucleic acid, respectively.
It is relatively easy to introduce a reactive site to an end of a nucleic acid. However, in light of the complexity of the synthesis of a nucleic acid base etc., when a modified DNA oligomer is synthesized by introducing a functional molecule to a nucleic acid base, it is general practice to introduce the functional molecule to a thymine base having an active site.
A method used widely for this purpose is to introduce an NHS (N-hydroxysuccinimide) group as an active site, and then introduce a functional molecule through a reaction with amine. Thus, a thymine base, which has no amino group, is suitable for the introduction of a functional molecule because a side reaction is less likely to occur (Non-Patent Document 1).